JP7124630B2 - Valve train with decompression device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a valve mechanism having a decompression device that performs a decompression operation to release pressure within a cylinder of an engine.

In a valve train of a four-cycle gasoline engine, a camshaft is provided with an exhaust-side cam for opening an exhaust valve during an exhaust stroke. A decompression device is provided on one side of the exhaust cam on the camshaft so as to be adjacent to the exhaust cam. A decompression device is a device that performs a decompression operation that improves engine startability by slightly opening an exhaust valve during a compression stroke at engine start-up to reduce the pressure in the cylinder.

The configuration of a conventional decompression device is roughly as follows. That is, the decompression device has a decompression shaft. A decompression pin projecting radially from the decompression shaft is provided on one end of the decompression shaft, and a decompression cam is formed on the other end of the decompression shaft to slightly open the exhaust valve during the compression stroke. Further, in the camshaft, a recess is formed in a portion extending from a portion of the outer peripheral surface of the camshaft to a portion of the base surface of the exhaust-side cam. The decompression shaft is housed within this recess. The decompression device also has a disk-shaped decompression holder with a hole formed in the center. The decompression holder is attached to the outer peripheral side of the camshaft by passing the camshaft through the central hole, and surrounds the decompression shaft and the outer peripheral side of the camshaft housed in the recess. Thereby, the decompression shaft is rotatably held in the recess. The decompression device also includes a decompression arm and a spring that biases the decompression arm. The decompression arm is arranged on the outer peripheral side of the camshaft, and is displaced away from the axis of the camshaft by centrifugal force when the camshaft rotates. The spring urges the decompression arm in a direction to bring it closer to the camshaft axis. A portion of the decompression arm is connected to the decompression pin. Thereby, the displacement of the decompression arm is transmitted to the decompression shaft via the decompression pin, and the displacement of the decompression arm is converted into rotation of the decompression shaft. Also, the decompression arm is attached to the decompression holder, and the spring is attached between the decompression holder and the decompression arm.

When the rotational speed of the camshaft is equal to or less than a predetermined rotational speed, the decompression arm is biased by the spring and positioned close to the shaft center of the camshaft. In this state, the decompression cam protrudes from the base surface of the exhaust cam. Therefore, in the compression stroke, the exhaust valve is slightly opened by the decompression cam, and the decompression operation is performed. On the other hand, when the rotation speed of the camshaft exceeds a predetermined rotation speed, the centrifugal force generated by the rotation of the camshaft displaces the decompression arm against the biasing force of the spring to a position away from the axis of the camshaft. do. As a result, the decompression shaft rotates, and the decompression cam sinks into the base surface of the exhaust side cam. Therefore, the exhaust valve is closed during the compression stroke, and the decompression operation is not performed.

An example of a conventional decompression device is described in Patent Document 1 below.

A conventional decompression device is assembled in the following manner. First, a camshaft, a decompression shaft, a decompression pin, a decompression holder, a decompression arm and a spring are prepared. The camshaft is provided with an exhaust-side cam in advance, and is formed with a recess for accommodating the decompression shaft. A decompression cam is formed in advance on the decompression shaft. Next, a decompression arm is attached to the decompression holder, and a spring is attached between the decompression holder and the decompression arm. Next, the decompression shaft is inserted into the recess formed in the camshaft. Next, the camshaft is inserted from one end side into the central hole of the decompression holder to which the decompression arm and the spring are attached, so that the decompression shaft and the outer peripheral side of the camshaft housed in the recess are surrounded. Install the decompression holder onto the camshaft. Next, the decompression pin is attached to the decompression shaft by press-fitting the decompression pin into a small-diameter attachment hole previously formed in the decompression shaft. Next, the decompression arm and the decompression pin are connected together.

Here, the decompression holder is arranged on one side of the exhaust side cam, and the diameter of the central hole of the decompression holder is smaller than the outer diameter of the exhaust side cam. Therefore, when assembling the decompression device, in order to attach the decompression holder to the camshaft, the camshaft must be inserted into the center hole of the decompression holder from one end side of the camshaft. That is, when the camshaft is inserted into the center hole of the decompression holder from the other end side of the camshaft, the decompression holder cannot be moved to one side of the exhaust side cam beyond the exhaust side cam.

JP-A-6-280531

In the conventional decompression device described above, when assembling the decompression device, the decompression shaft must be inserted into the recess of the camshaft, and the decompression pin must be attached to the decompression shaft after the decompression holder is attached to the camshaft. That is, the decompression pin is attached so as to radially protrude from the peripheral surface of the decompression shaft on one end side. The position at which the decompression holder is attached to the camshaft is generally a position facing the axially central portion of the decompression shaft. Therefore, if the decompression pin is attached to the decompression shaft, the decompression shaft is inserted into the concave portion of the camshaft, and then the camshaft is inserted into the center hole of the decompression holder from one end side, the decompression pin hits the decompression holder. The decompression holder cannot be moved beyond the decompression pin to a position facing the axial center of the decompression shaft. Therefore, in the conventional decompression device, there is no choice but to adopt an assembly method of inserting the decompression shaft into the concave portion of the camshaft, mounting the decompression holder on the camshaft, and then attaching the decompression pin to the decompression shaft.

However, the assembly method of attaching the decompression pin to the decompression shaft after inserting the decompression shaft into the concave portion of the camshaft and attaching the decompression holder to the camshaft has the following problems.

That is, in a state in which the decompression shaft is inserted into the concave portion of the camshaft, pressure is applied to the decompression pin for press-fitting the decompression pin into the mounting hole of the decompression shaft, so the pressure is also applied to the camshaft. Therefore, the hardness or strength of the camshaft must be increased to withstand the pressure. Moreover, when the decompression pin is attached to the decompression shaft in a state where the decompression shaft is inserted into the concave portion of the camshaft, it is difficult to determine the attachment position or attachment angle of the decompression pin with respect to the decompression shaft with high accuracy. In addition, when the decompression pin is press-fitted into the mounting hole of the decompression shaft inserted into the concave portion of the camshaft, it is necessary to grip the decompression pin. It is necessary to increase the amount of protrusion of the decompression pin from the decompression shaft. As a result, the overall outer diameter of the decompression device becomes large, and the decompression device becomes large.

The present invention has been made in view of the above problems, for example, and an object of the present invention is to provide a decompression device assembly method in which a decompression shaft is inserted into a concave portion of a camshaft and a decompression holder is attached to the camshaft. Later, the method of attaching a decompression pin to the decompression shaft will be abolished, and instead, a method of mounting the decompression holder on the camshaft after inserting the decompression shaft provided with the decompression pin into the concave portion of the camshaft can be adopted. An object of the present invention is to provide a valve mechanism.

In order to solve the above-mentioned problems, the present invention provides a valve train including a camshaft provided with an exhaust-side cam, and a decompression device arranged on one side of the exhaust-side cam in the axial direction of the camshaft. A decompression shaft extending in the axial direction of the camshaft over a part of the camshaft peripheral surface and a part of the base surface of the exhaust side cam is attached to the camshaft and the exhaust side cam. A housing recess is formed, and the decompression device is formed in an outer cylindrical shape having an axis extending in the axial direction of the camshaft, and is arranged in the decompression shaft housing recess, and the decompression shaft is arranged in the axial direction of the decompression shaft. A decompression pin provided on one side portion so as to protrude radially from the peripheral surface of the decompression shaft, and a decompression cam formed on the other side portion of the decompression shaft in the axial direction and protruding with respect to the base surface of the exhaust side cam. is formed in a ring shape or a C shape so as to surround the outer peripheral sides of the camshaft and the decompression shaft, and is provided at a position substantially facing the axially central portion of the decompression shaft so as to connect the decompression shaft to the decompression shaft. a decompression holder rotatably held in the shaft housing recess; and a decompression holder provided on the outer peripheral side of the camshaft, connected to the decompression pin, and displaced away from the camshaft by centrifugal force generated when the camshaft rotates. a decompression arm that rotates the decompression shaft via the decompression pin; and a biasing member that biases the decompression arm in a direction to approach the camshaft. When the decompression holder is attached to the camshaft, the decompression holder is attached to the decompression shaft arranged in the decompression shaft housing recess from one end side of the camshaft on one or both of the outer peripheral surfaces of the A pin passing portion, which is a groove or recess for passing the decompression pin when the decompression shaft is moved to the outer peripheral side of the axially central portion of the decompression shaft beyond the provided decompression pin, is formed.

According to the present invention, as a method of assembling the decompression device, it is possible to adopt a method of mounting the decompression holder on the camshaft after inserting the decompression shaft provided with the decompression pin into the concave portion of the camshaft.

1 is an external view showing an engine provided with a valve train according to an embodiment of the present invention; FIG. FIG. 2 is an explanatory view of the inside of the cylinder head of the engine in FIG. 1 as seen from above; 3 is an explanatory view showing a state in which the intake side rocker shaft, the intake side rocker arm, the exhaust side rocker shaft, the exhaust side rocker arm, and the shaft support portion are removed from the inside of the cylinder head in FIG. 2; FIG. FIG. 3 is a cross-sectional view showing the cylinder head and the cylinder head cover as seen from the direction of arrows IV-IV in FIG. 2; 1 is a perspective view showing a camshaft, an intake-side cam, and an exhaust-side cam in a valve mechanism of an embodiment of the present invention; FIG. 6 is a cross-sectional view showing the camshaft and the exhaust side cam as viewed in the direction of arrows VI-VI in FIG. 5; FIG. 1 is a perspective view showing a camshaft, an intake-side cam, an exhaust-side cam, and a decompression device in a valve mechanism according to an embodiment of the present invention; FIG. FIG. 8 is an explanatory view showing a camshaft, a decompression device, etc., viewed from the direction of arrow VIII in FIG. 7; FIG. 9 is an explanatory view showing a camshaft, a decompression device, etc., viewed from the direction of arrow IX in FIG. 8; FIG. 3 is a perspective view showing a decompression shaft, a decompression pin and a decompression cam in the decompression device of the valve mechanism of the embodiment of the present invention; FIG. 4 is an explanatory view showing a decompression holder in the decompression device of the valve mechanism of the embodiment of the present invention; FIG. 12 is a cross-sectional view showing the decompression holder viewed from the direction of arrows XII-XII in FIG. 11; FIG. 4 is an explanatory diagram showing the operation of the decompression device in the valve mechanism of the embodiment of the invention; It is explanatory drawing which shows the assembly method of the decompression apparatus in the valve mechanism of the Example of this invention. It is explanatory drawing which shows the assembly method of the decompression apparatus in the valve mechanism of the Example of this invention. It is explanatory drawing which shows the assembly method of the decompression apparatus in the valve mechanism of the Example of this invention. It is explanatory drawing which shows the assembly method of the decompression apparatus in the valve mechanism of the Example of this invention. FIG. 4 is an explanatory view showing two positions of a decompression shaft inserted into a decompression shaft housing recess in the assembly process of the decompression device in the valve mechanism of the embodiment of the present invention; FIG. 11 is an explanatory diagram showing a decompression holder in a decompression device for a valve train according to another embodiment of the present invention; FIG. 11 is an explanatory diagram showing a camshaft of a valve mechanism of still another embodiment of the present invention; FIG. 11 is an explanatory diagram showing a decompression holder in a decompression device for a valve train according to another embodiment of the present invention;

A valve mechanism according to an embodiment of the present invention includes a camshaft provided with an exhaust-side cam, and a decompression device arranged on one side of the exhaust-side cam in the axial direction of the camshaft. A decompression shaft housing recess extending in the axial direction of the camshaft is formed in the camshaft and the exhaust side cam over a portion of the peripheral surface of the camshaft and a portion of the base surface of the exhaust side cam. The decompression device includes a decompression shaft, a decompression pin, a decompression cam, a decompression holder, a decompression arm and a biasing member.

The decompression shaft has a cylindrical outer shape with an axis extending in the axial direction of the camshaft, and is disposed in the decompression shaft housing recess. The decompression pin is provided on one axial side portion of the decompression shaft so as to radially protrude from the peripheral surface of the decompression shaft. The decompression cam is formed on the other axial side portion of the decompression shaft, and protrudes and retracts with respect to the base surface of the exhaust side cam. The decompression holder is formed in a ring shape or a C-shape so as to surround the outer peripheral sides of the camshaft and the decompression shaft, and is provided at a position facing substantially the center of the decompression shaft in the axial direction. rotatably held inside. The decompression arm is provided on the outer peripheral side of the camshaft, is connected to the decompression pin, and rotates the decompression shaft via the decompression pin by being displaced away from the camshaft by centrifugal force generated when the camshaft rotates. The biasing member biases the decompression arm toward the camshaft.

In addition, one or both of the inner peripheral surface of the decompression holder and the outer peripheral surface of the camshaft are provided with a decompression holder that can be inserted into the decompression shaft housing recess from one end of the camshaft when the decompression holder is attached to the camshaft. A pin passing portion, which is a groove or a concave portion, is formed for passing the decompression pin when the decompression shaft is moved to the outer peripheral side of the axially central portion of the decompression shaft beyond the decompression pin provided on the arranged decompression shaft.

In the valve mechanism according to the embodiment of the present invention, the decompression device is assembled according to the conventional method. The method of attaching a decompression pin can be eliminated, and instead, the following method, for example, can be adopted. First, install the decompression pin on the decompression shaft. Alternatively, a decompression shaft integrally formed with a decompression pin is prepared. Also, a decompression arm and a biasing member are attached to the decompression holder. Next, the decompression shaft provided with the decompression pin is inserted into the decompression shaft housing recess. Next, the camshaft is inserted from one end side of the camshaft into the inside of the decompression holder formed in a ring shape or a C shape, and the decompression holder is moved to the outer peripheral side of the substantially central portion in the axial direction of the decompression shaft, Install on the camshaft. Next, the decompression arm and the decompression pin are connected together.

According to the valve mechanism of the embodiment of the present invention, the decompression holder is mounted on the camshaft because the pin holes are formed in one or both of the inner peripheral surface of the decompression holder and the outer peripheral surface of the camshaft. Sometimes, a decompression pin provided on a decompression shaft disposed within the decompression shaft housing recess can be passed through the pin passage. Therefore, the decompression holder can be moved from the one end side of the camshaft to the outer peripheral side of the decompression shaft substantially in the axial direction over the decompression pin provided on the decompression shaft arranged in the decompression shaft housing recess.

According to the valve mechanism of the embodiment of the present invention, the decompression pin can be attached to the decompression shaft before the decompression shaft is inserted into the decompression shaft housing recess, or the decompression shaft integrally formed with the decompression pin is used. be able to. As a result, the step of press-fitting the decompression pin into the mounting hole of the decompression shaft while the decompression shaft is inserted into the decompression shaft housing recess can be eliminated. There is no need to consider the pressure when press-fitting the decompression shaft into the mounting hole. Also, the attachment position or attachment angle of the decompression pin to the decompression shaft can be determined at a stage before the decompression shaft is inserted into the decompression shaft housing recess. Therefore, the accuracy of the mounting position or mounting angle of the decompression pin relative to the decompression shaft can be improved compared to the case where the mounting position or mounting angle of the decompression pin relative to the decompression shaft is determined while the decompression shaft is inserted into the decompression shaft housing recess. can be done. In addition, since the process of press-fitting the decompression pin into the mounting hole of the decompression shaft inserted into the decompression shaft housing recess can be eliminated, the amount of protrusion of the decompression pin from the decompression shaft can be reduced in consideration of gripping the decompression pin in this process. No need to increase. Therefore, the overall outer diameter of the decompression device can be reduced, and the size of the decompression device can be reduced.

First, the engine and the valve mechanism in the embodiment of the present invention will be outlined. FIG. 1 shows an engine 1 provided with a valve train according to an embodiment of the invention. The engine 1 is, for example, a four-cycle gasoline engine for a straddle-type vehicle. As shown in FIG. 1, the engine 1 includes a crankcase 3 housing a crankshaft and the like, a cylinder 4 housing a piston and the like, and a cylinder head 5 housing an exhaust valve, an intake valve, a valve mechanism, and the like. and a cylinder head cover 6 that covers the cylinder head 5 from above.

FIG. 2 shows a top view of the cylinder head 5 with the cylinder head cover 6 removed. 3 shows a state in which the intake side rocker arm 15, the exhaust side rocker arm 16, the intake side rocker shaft 20, the exhaust side rocker shaft 21, the shaft support portion 22, etc. are removed from the cylinder head 5 in FIG. . FIG. 4 shows a cross section of the cylinder head 5, the cylinder head cover 6 and the valve mechanism 11 as seen from the direction of arrow IV-IV in FIG.

As shown in FIGS. 3 and 4, two intake valves 7 and two exhaust valves 8 are provided within the cylinder head 5 . The engine 1 in this embodiment is a two-valve two-cylinder engine, and each cylinder is provided with one intake valve 7 and one exhaust valve 8 . Each intake valve 7 is biased by a valve spring 9 to close the intake port. Each exhaust valve 8 is biased by a valve spring 10 so as to close the exhaust port.

A valve mechanism 11 for controlling the opening and closing of each intake valve 7 and each exhaust valve 8 is provided in the cylinder head 5 . The valve mechanism 11 in this embodiment is of the SOHC type and has a single camshaft 12 . The camshaft 12 is provided with an intake cam 13 that controls opening and closing of each intake valve 7 and an exhaust cam 14 that controls opening and closing of each exhaust valve 8 . The intake side cam 13 is provided on the left side of the camshaft 12 in the axial direction, and the exhaust side cam 14 is provided on the substantially central portion of the camshaft 12 in the axial direction. The intake side cam 13 and the exhaust side cam 14 are formed integrally with the camshaft 12 . A decompression device 41 is provided on one side of the exhaust cam 14 in the axial direction of the camshaft 12 , that is, on the right side of the exhaust cam 14 .

Further, as shown in FIG. 2, the valve mechanism 11 includes an intake-side rocker arm 15 that pushes each intake valve 7 according to rotation of the intake-side cam 13, and each exhaust valve 8 according to rotation of the exhaust-side cam 14. It has an exhaust-side rocker arm 16 that pushes the . A roller 17 is provided at one end of the intake-side rocker arm 15 , and the peripheral surface of the roller 17 is in contact with the peripheral surface of the intake-side cam 13 . Further, the other bifurcated ends of the intake-side rocker arm 15 are in contact with adjusting members 19 such as shims provided on the stem end side of the intake valve 7 . Similarly, a roller 18 is provided at one end of the exhaust-side rocker arm 16 , and the peripheral surface of the roller 18 is in contact with the peripheral surface of the exhaust-side cam 14 . In addition, the other bifurcated ends of the exhaust-side rocker arm 16 are in contact with adjusting members 19 provided on the stem end side of the exhaust valve 8 . The intake-side rocker arm 15 and the exhaust-side rocker arm 16 are rotatably supported by an intake-side rocker shaft 20 and an exhaust-side rocker shaft 21, respectively.

Both axial end portions of the camshaft 12 , the intake-side rocker shaft 20 , and the exhaust-side rocker shaft 21 are supported by the cylinder head 5 by a pair of shaft support portions 22 . Specifically, both axial end portions of the camshaft 12 are rotatably supported by respective shaft support portions 22 . The intake-side rocker shaft 20 and the exhaust-side rocker shaft 21 are arranged above the camshaft 12 , and their axial end portions are fixed by shaft support portions 22 . A cam sprocket is provided at the right end of the camshaft 12 in FIG. 2, and a timing chain 23 (or a timing belt) is hooked on the cam sprocket.

Next, the camshaft 12, the exhaust side cam 14 and the decompression device 41 in the embodiment of the present invention will be explained. In the description of the camshaft 12, the exhaust-side cam 14, and the decompression device 41, for convenience of explanation, the axial direction of the camshaft 12 will be referred to as the "X direction". One side in the direction is called "X1 side", and the other side in the X direction is called "X2 side". Further, the direction perpendicular to the X direction is called the "Y direction", one side in the Y direction is called the "Y1 side", and the other side in the Y direction is called the "Y2 side. A direction perpendicular to both the X direction and the Y direction is called the "Z direction", and as indicated by the arrows in FIGS. The other side is called "Z2 side".

FIG. 5 shows the camshaft 12, the exhaust side cam 14, and the like. FIG. 6 shows the camshaft 12 and the exhaust side cam 14 viewed from the direction of arrows VI--VI in FIG. As shown in FIG. 5, on the peripheral surface of the exhaust side cam 14, a base surface 14A is formed on the Y1 side, and a projecting surface 14B is formed on the Y2 side. The base surface 14A is a portion of the peripheral surface of the exhaust cam 14 along a circle about the axis of the camshaft 12 . The protruding surface 14B is a portion of the peripheral surface of the exhaust cam 14 that protrudes outward from a circle about the axis of the camshaft 12 .

Further, the camshaft 12 is formed with a decompression shaft housing recess 25 for housing the decompression shaft 42 of the decompression device 41 . The decompression shaft housing recess 25 extends in the X direction so as to cover the Y1 side portion of the outer peripheral surface of the camshaft 12 and the Y1 side portion of the base surface 14A of the exhaust side cam 14 .

A pin through recess 26 is formed on the outer peripheral surface of the camshaft 12 . When the decompression holder 45 is attached to the camshaft 12 , the pin through recess 26 is inserted into the decompression holder 45 from one end side of the camshaft 12 . is a recess (pin passage portion) through which the decompression pin 43 is passed when the decompression shaft 42 is moved to the outer peripheral side of the substantially central portion in the axial direction of the decompression shaft 42 . The pin through recess 26 is arranged on the X1 side of the decompression shaft housing recess 25 and at a position adjacent to the decompression shaft housing recess 25 substantially on the Z2 side of the decompression shaft housing recess 25 (one circumferential side of the camshaft 12). , and the decompression shaft housing recess 25 . As shown in FIG. 6, the bottom surface of the pin through recess 26 is continuous with the bottom surface of the decompression shaft accommodating recess 25, and these bottom surfaces are on the same plane.

A fixing pin mounting hole 27 for mounting a holder fixing pin 31 that locks the decompression holder 45 to the camshaft 12 so as not to rotate is formed in the Y2 side portion of the outer peripheral surface of the camshaft 12 . One end of the holder fixing pin 31 is fitted in the fixing pin mounting hole 27 . The other end side of the holder fixing pin 31 protrudes radially from the Y2 side portion of the outer peripheral surface of the camshaft 12 . Further, as shown in FIG. 5, on the outer peripheral surface of the camshaft 12, a clip mounting groove 30 for mounting a washer 28 and a circlip 29 is formed on the entire circumference of the camshaft 12 on the X1 side of the decompression shaft housing recess 25. is formed over

FIG. 7 shows a decompression device 41 provided on the camshaft 12. As shown in FIG. FIG. 8 shows the decompression device 41 viewed from the direction of arrow VIII in FIG. FIG. 9 shows the decompression device 41 viewed from the direction of arrow IX in FIG. As shown in FIGS. 7 to 9, the decompression device 41 includes a decompression shaft 42, a decompression pin 43, a decompression cam 44, a decompression holder 45, a decompression arm 58 and a coil spring 63.

The decompression shaft 42 is arranged in the decompression shaft housing recess 25 . The decompression pin 43 is provided on the X1 side of the decompression shaft 42 , and the decompression cam 44 is formed on the X2 side of the decompression shaft 42 . Here, FIG. 10 shows the decompression shaft 42, the decompression pin 43 and the decompression cam 44. As shown in FIG. As shown in FIG. 10, the decompression shaft 42 is made of, for example, a metal material and has a cylindrical shape with an axis extending in the X direction. The decompression pin 43 is, for example, a rod-shaped member made of metal, and is provided on the X1 side portion of the decompression shaft 42 so as to protrude radially from the peripheral surface of the decompression shaft 42 . The decompression pin 43 can be provided on the decompression shaft 42 by press-fitting the base end portion of the decompression pin 43 into a hole formed in the peripheral surface of the decompression shaft 42 on the X1 side. Alternatively, the decompression shaft 42 and the decompression pin 43 may be integrally formed by molding or the like. Alternatively, the decompression pin 43 can be joined to the decompression shaft 42 by welding. On the other hand, the decompression cam 44 is formed at the end of the decompression shaft 42 on the X2 side, and has a flat portion 44A and a curved surface portion 44B.

As shown in FIG. 9 , the X1 side portion of the decompression shaft 42 provided with the decompression pin 43 is arranged in a portion of the decompression shaft accommodation recess 25 located on the outer peripheral surface of the camshaft 12 . Also, the decompression cam 44 is arranged in a portion of the decompression shaft housing recess 25 that is positioned on the base surface 14A of the exhaust side cam 14 . As the decompression shaft 42 rotates within the decompression shaft housing recess 25 , the decompression cam 44 appears and disappears with respect to the base surface 14</b>A of the exhaust side cam 14 .

As shown in FIG. 7, the decompression holder 45 is provided at a position facing the substantially central portion of the decompression shaft 42 in the axial direction, and surrounds the camshaft 12 and the decompression shaft 42 on the outer peripheral side. The decompression holder 45 is a member mainly having a function of rotatably holding the decompression shaft 42 in the decompression shaft housing recess 25 and a function of supporting the decompression arm 58 . Here, FIG. 11 shows the decompression holder 45, and FIG. 12 shows a cross section of the decompression holder 45 viewed from the arrow XII--XII direction in FIG. As shown in FIG. 11, the decompression holder 45 is made of, for example, a metal material and has a ring shape. The inner diameter of the decompression holder 45 is slightly larger than the outer diameter of the camshaft 12 . For example, the difference between the inner diameter of the decompression holder 45 and the outer diameter of the camshaft 12 is greater than 0 mm and equal to or less than 0.1 mm.

A decompression shaft cover groove 46 is formed at a position facing the decompression shaft housing recess 25 on the inner peripheral surface of the decompression holder 45 so as to cover the portion of the decompression shaft 42 that protrudes from the decompression shaft housing recess 25 . It is A bottom surface of the decompression shaft cover groove 46 is formed in an arc shape along the outer peripheral surface of the decompression shaft 42 .

A pin through groove 47 is formed in the inner peripheral surface of the decompression holder 45 . When the decompression holder 45 is attached to the camshaft 12 , the pin through groove 47 is inserted into the decompression pin 43 provided in the decompression shaft 42 arranged in the decompression shaft housing recess 25 from one end side of the camshaft 12 . is a groove (pin passage portion) through which the decompression pin 43 is passed when the decompression shaft 42 is moved to the outer peripheral side of the substantially central portion in the axial direction. The pin through groove 47 is adjacent to the decompression shaft covering groove 46 on the Z2 side of the decompression shaft covering groove 46 (one circumferential side of the decompression holder 45 ), and is integrated with the decompression shaft covering groove 46 . The bottom surface of the pin through groove 47 and the bottom surface of the decompression shaft covering groove 46 are connected to each other, and the portion of the inner peripheral surface of the decompression holder 45 where the pin through groove 47 and the decompression shaft covering groove 46 are formed is continuous. concave.

An arm support portion 49 for rotatably supporting the shaft support portion 59 of the decompression arm 58 is provided on the Y2 side portion of the decompression holder 45 . At the center of the arm support portion 49, there is an insertion hole 51 for attaching the shaft support portion 59 of the decompression arm 58 to the decompression holder 45 and for inserting the support member 50 (see FIG. 7) serving as the rotation shaft of the decompression arm 58. formed.

A weight portion 52 is formed on the Z2 side of the decompression holder 45 . The weight portion 52 is a portion for balancing the weight around the rotational axis of the camshaft 12 with the decompression device 41 attached to the camshaft 12 . As shown in FIG. 12, the weight portion 52 is formed integrally with the Z2 side portion of the decompression holder 45. More specifically, the Z2 side portion of the decompression holder 45 is made thicker than the other portions. formed.

A spring hook 53 is attached to the Z2 side of the decompression holder 45 . The spring hook 53 is a member for attaching the end of the coil spring 63 . The spring hook 53 is made of, for example, a metal plate. A spring hooking portion 54 for hooking the end portion of the coil spring 63 is formed on the Y2 side end portion 53A of the spring hook 53 . The Y2-side end portion 53A of the spring hook 53 is rotatably supported by the decompression holder 45, and the Y1-side end portion 53B of the spring hook 53 is engaged with a convex locking portion 55 formed in the decompression holder 45. Locked.

A holder groove portion 56 having a shape recessed in the radial direction of the camshaft 12 is formed on the Y2 side portion of the inner peripheral surface of the decompression holder 45 . A projecting end of the holder fixing pin 31 attached to the fixing pin attaching hole 27 of the camshaft 12 is inserted into the holder groove 56 . The holder groove 56 and the projecting end of the holder fixing pin 31 are fitted together, so that when the camshaft 12 rotates while the engine 1 is running, the decompression holder 45 rotates together with the camshaft 12 .

8, the decompression arm 58 is a member that rotates the decompression shaft 42 via the decompression pin 43 by being displaced away from the camshaft 12 by centrifugal force generated when the camshaft 12 rotates. The decompression arm 58 is an arcuate member made of, for example, a metal material. A shaft support portion 59 for rotatably attaching the decompression arm 58 to the arm support portion 49 of the decompression holder 45 via the support member 50 is formed at the Y2 side end portion of the decompression arm 58 . The decompression arm 58 is attached to the decompression holder 45 so as to be arranged on the outer Z1 side of the camshaft 12 . A stopper 60 is formed at the Y2 side end of the decompression arm 58 to limit the amount of displacement of the decompression arm 58 in the direction away from the camshaft 12 . A spring hooking hole 61 for hooking the end of the coil spring 63 is formed in the Y2 side end of the decompression arm 58 . A connection groove 62 for connecting the decompression arm 58 and the decompression pin 43 is formed at the Y1 side end of the decompression arm 58 . The decompression arm 58 and the decompression pin 43 are coupled by inserting the projecting end of the decompression pin 43 into the coupling groove 62 .

Also, the coil spring 63 is a biasing member that biases the decompression arm 58 in a direction to approach the camshaft, and one end thereof is connected to the spring hooking portion 54 of the spring hook 53 provided on the decompression holder 45. The other end is connected to the spring hooking hole 61 of the decompression arm 58 .

Further, as shown in FIG. 9, a washer 28 and a circlip 29 are attached to a clip attachment groove 30 formed in the camshaft 12 . The circlip 29 and washer 28 mainly function to prevent the decompression shaft 42 and decompression holder 45 from moving toward the X1 side.

The operation of the decompression device 41 is as follows. 13A and 13B show cross sections of the exhaust side cam 14 and the decompression cam 44 as seen from the direction of arrows XIII-XIII in FIG. In FIG. 13A, while the rotation speed of the camshaft 12 is equal to or less than a predetermined rotation speed, the inner peripheral surface of the decompression arm 58 contacts the outer peripheral surface of the camshaft 12 due to the biasing force of the coil spring 63. It is closest to the axis of camshaft 12 . In this state, the projecting end side of the decompression pin 43 connected to the decompression arm 58 is inclined toward the Z2 side, and the curved surface portion 44B of the decompression cam 44 faces the Y1 side. As a result, the decompression cam 44 protrudes from the base surface 14A of the exhaust cam 14 . Thereby, a decompression operation is performed. On the other hand, in FIG. 13B, when the rotation speed of the camshaft 12 exceeds a predetermined rotation speed, the decompression arm 58 resists the biasing force of the coil spring 63 due to the centrifugal force generated when the camshaft 12 rotates. , is displaced away from the camshaft 12 , and the stopper 60 of the decompression arm 58 contacts the outer peripheral surface of the camshaft 12 . In this state, the projecting end side of the decompression pin 43 connected to the decompression arm 58 inclines toward the Z1 side, and the flat portion 44A of the decompression cam 44 faces toward the Y1 side. As a result, the decompression cam 44 sinks into the base surface 14A of the exhaust cam 14 . This prevents the decompression operation from being performed.

14 to 17 show each step in the method of assembling the decompression device 41. FIG. 18 shows two positions of the decompression shaft 42 inserted into the decompression shaft housing recess 25 in the process of assembling the decompression device 41. As shown in FIG. A method of assembling the decompression device 41 is as follows.

First, as parts of the decompression device 41, the camshaft 12, the decompression shaft 42, the decompression holder 45, the decompression arm 58 and the coil spring 63 are prepared. The components shown in FIGS. 5 and 6, such as the intake side cam 13, the exhaust side cam 14, the decompression shaft housing recess 25, the pin through recess 26, and the fixing pin mounting hole 27, are formed in advance on the camshaft 12. . A holder fixing pin 31 is attached in advance to the fixing pin attachment hole 27 of the camshaft 12 . As shown in FIG. 10, the decompression shaft 42 is provided with a decompression pin 43 in advance by means of press-fitting, molding, welding, or the like, and a decompression cam 44 is formed in advance. As shown in FIG. 11, the decompression holder 45 is preformed with a decompression shaft cover groove 46, a pin insertion groove 47, and the like, and a spring hook 53 is attached in advance.

Next, the decompression arm 58 and the coil spring 63 are attached to the decompression holder 45 (decompression arm attachment step).

Next, as shown in FIG. 14, the decompression shaft 42 provided with the decompression pin 43 is inserted into the decompression shaft housing recess 25 of the camshaft 12 (decompression shaft insertion step). At this time, the decompression shaft 42 is arranged in the decompression shaft housing recess 25 and the decompression pin 43 is arranged in the pin through recess 26 as indicated by the two-dot chain lines in FIGS. 18A and 6 . That is, as shown in FIG. 18A, the decompression shaft accommodation recess 25 is formed such that its length in the X direction is longer than the length of the decompression shaft 42 in the X direction (axial direction). This is done so that the decompression shaft 42 is moved in the X direction while being arranged in the decompression shaft accommodation recess 25 so that the decompression pin 43 provided on the decompression shaft 42 can be inserted into and removed from the connection groove 62 of the decompression arm 58 . It is for When the decompression shaft 42 is inserted into the decompression shaft housing recess 25, the decompression shaft 42 is arranged so as to approach the end of the decompression shaft housing recess 25 on the X1 side, as indicated by the two-dot chain line in FIG. 18(A). do. 6, when the decompression shaft 42 is inserted into the decompression shaft accommodating recess 25, the protruding end side of the decompression pin 43 provided on the decompression shaft 42 falls into the pin insertion recess 26. , the decompression shaft 42 is arranged.

Next, as shown in FIG. 15, the camshaft 12 is inserted from the X1 side of the camshaft 12 into the decompression holder 45 to which the decompression arm 58 and the coil spring 63 are attached. Subsequently, the decompression holder 45 is passed through the position P corresponding to the X1 side end portion where the decompression pin 43 is provided in the decompression shaft 42 inserted into the decompression shaft housing recess 25 , and is inserted into the decompression shaft housing recess 25 . It is moved to the X2 side until it reaches the position Q facing the substantially intermediate portion of the decompression shaft 42 in the axial direction (decompression holder insertion step).

While the decompression holder 45 is moved in this manner, when the decompression holder 45 reaches position P, the pin insertion groove 47 of the decompression holder 45 and the pin insertion recess 26 of the camshaft 12 face each other in the Y direction. At this time, as shown in FIG. 11, a gap 48 through which the decompression pin 43 can pass (hereinafter referred to as a "pin through gap") is formed between the pin through groove 47 and the pin through recess 26. . The decompression pin 43 can pass through the pin through gap 48 without contacting the decompression holder 45 . That is, the decompression holder 45 can pass through the Y1 side of the decompression pin 43 arranged in the pin through recess 26 without contacting the decompression pin 43 . Therefore, the decompression holder 45 can move over the decompression pin 43 to the X2 side and reach the position Q. As shown in FIG.

Further, when the decompression holder 45 is moved to the position Q, the projecting end of the holder fixing pin 31 is inserted into the holder groove 56 and both are fitted.

Subsequently, as indicated by the arrow in FIG. 16, the decompression pin 43 arranged in the pin through recess 26 is raised, and then the decompression shaft 42 is slid to the X2 side (see also FIG. 18(B)), As shown in FIG. 17, the decompression pin 43 is inserted into the connecting groove 62 of the decompression arm 58 . Thereby, the decompression arm 58 and the decompression pin 43 are connected (decompression pin connection step).

Subsequently, as shown in FIG. 9, the washer 28 and the circlip 29 are attached to the clip attachment groove 30 formed in the camshaft 12 (clip attachment step). This completes the assembly of the decompression device 41 .

As described above, according to the valve mechanism 11 of the embodiment of the present invention, the pin through groove 47 is formed on the inner peripheral surface of the decompression holder 45 and the pin through recess 26 is formed on the outer peripheral surface of the camshaft 12. When the decompression holder 45 is attached to the camshaft 12 , a pin through gap 48 through which the decompression pin 43 provided on the decompression shaft 42 arranged in the decompression shaft housing recess 25 can pass is formed on the inner periphery of the decompression holder 45 . It can be formed between the surface and the outer peripheral surface of the camshaft 12 . Therefore, as a method for assembling the decompression device 41, as shown in FIGS. It is possible to adopt a method such as

According to such an assembly method, the decompression pin 43 can be attached to the decompression shaft 42 before assembling the decompression device 41, or the decompression shaft 42 integrally formed with the decompression pin 43 can be used. Therefore, the accuracy of the position and projection angle of the decompression pin 43 with respect to the decompression shaft 42 can be improved. In addition, the conventional assembly method of inserting the decompression shaft into the concave portion of the camshaft and mounting the decompression holder on the camshaft and then press-fitting the decompression pin into the decompression shaft can be eliminated. It is no longer necessary to set the hardness or strength of the camshaft in consideration of the pressure applied to the camshaft when turning. Further, in the conventional assembly method described above, it was necessary to lengthen the decompression pin in order to hold the decompression pin when the decompression pin was press-fitted into the decompression shaft during assembly of the decompression device, but this is not necessary in the present embodiment. . Therefore, the decompression pin 43 can be shortened, so that the overall outer diameter of the decompression device 41 can be reduced. Therefore, the decompression device can be miniaturized.

Further, in the valve mechanism 11 of the embodiment of the present invention, the pin through groove 47 is formed in the inner peripheral surface of the decompression holder 45, the pin through recess 26 is formed in the outer peripheral surface of the camshaft 12, and the pin through groove 47 is formed. and the pin through recesses 26 form the pin through gaps 48, compared to the case where the pin through gaps 48 are formed only by forming the pin through grooves 47 on the inner peripheral surface of the decompression holder 45, The depth dimension of the pin through groove 47, that is, the length dimension of the pin through groove 47 in the radial direction of the camshaft 12 can be reduced. Therefore, when the inner peripheral surface of the decompression holder 45 is cut away to form the pin through grooves 47, the extent to which the inner peripheral surface of the decompression holder 45 is cut can be reduced. Therefore, the outer diameter of the decompression holder 45 can be reduced while ensuring sufficient strength of the decompression holder 45, and the decompression device 41 can be miniaturized. In addition, since the outer diameter of the decompression holder 45 provided on the outer peripheral side of the camshaft 12 can be reduced, the moment of inertia during rotation of the camshaft 12 can be suppressed, and the rotation of the camshaft 12 can be stabilized.

Further, in the valve mechanism 11 of the embodiment of the present invention, the pin through groove 47 is adjacent to the decompression shaft covering groove 46 in the circumferential direction of the decompression holder 45 and integrated with the decompression shaft covering groove 46 . The pin through recess 26 is arranged on one end side of the decompression shaft housing recess 25 in the axial direction of the camshaft 12 and at a position adjacent to the decompression shaft housing recess 25 in the circumferential direction of the camshaft 12 to accommodate the decompression shaft. It is integrated with the recess 25 . With these configurations, when the decompression holder 45 is attached to the outer peripheral side of the camshaft 12 , the decompression pin 43 can be stably pushed into the pin insertion recess 26 and passed through the pin insertion gap 48 . Therefore, it is possible to prevent the decompression pin 43 from moving and coming into contact with the decompression holder 45 when the decompression pin 43 is passed through the pin insertion gap 48 . Therefore, the decompression pin 43 can be smoothly passed through the pin insertion gap 48, and workability in assembling the decompression device 41 can be enhanced.

In the above-described embodiment, the pin insertion groove 47 is formed on the inner peripheral surface of the decompression holder 45, and the pin insertion recess 26 is formed on the outer peripheral surface of the camshaft 12. However, the present invention is not limited to this. . Like the decompression holder 71 and the camshaft 72 shown in FIG. 19, the pin insertion groove 73 may be formed on the inner peripheral surface of the decompression holder 71 and the pin insertion recess may not be formed on the outer peripheral surface of the camshaft 72. . With this configuration as well, when the decompression holder 71 is attached to the camshaft 72, the pin through gap 74 through which the decompression pin 43 provided on the decompression shaft 42 disposed in the decompression shaft housing recess 25 can pass is formed in the decompression holder. It can be formed between the pin through groove 73 of 71 and the outer peripheral surface of the camshaft 72 .

Also, like the camshaft 81 and the decompression holder 82 shown in FIG. 20, the pin insertion recess 83 is formed on the outer peripheral surface of the camshaft 81, and the pin insertion groove is not formed on the inner peripheral surface of the decompression holder 82. good too. With this configuration as well, when the decompression holder 82 is attached to the camshaft 81, the pin through gap 84 through which the decompression pin 43 provided on the decompression shaft 42 disposed in the decompression shaft housing recess 25 can be passed is provided. It can be formed between the pin through recess 83 of 72 and the inner peripheral surface of the decompression holder 71 .

Further, as shown in FIG. 21, the decompression holder 91 having the decompression shaft cover groove 46 and the pin insertion groove 47 may be formed in a C shape.

Further, the valve mechanism of the present invention is not limited to engines for straddle-type vehicles, and can be applied to various engines such as engines for outboard motors.

In addition, the present invention can be modified as appropriate within the scope not contrary to the gist or idea of the invention that can be read from the scope of claims and the entire specification, and the valve train that accompanies such modifications is also the technical concept of the present invention. include.

REFERENCE SIGNS LIST 11 valve mechanism 12, 72, 81 camshaft 14 exhaust side cam 14A base surface 25 decompression shaft accommodation recess 26, 83 pin through recess (pin through portion)
41 decompression device 42 decompression shaft 43 decompression pin 44 decompression cam 45, 71, 82, 91 decompression holder 46 decompression shaft cover groove 47, 73 pin through groove (pin through portion)
48 Pin through gap 58 Decompression arm 63 Coil spring

Claims (4)

A valve mechanism comprising a camshaft provided with an exhaust-side cam and a decompression device arranged on one side of the exhaust-side cam in the axial direction of the camshaft,
The camshaft and the exhaust-side cam are formed with a decompression shaft accommodating recess extending in the axial direction of the camshaft over a portion of the peripheral surface of the camshaft and a portion of the base surface of the exhaust-side cam. is,
The decompression device is
a decompression shaft formed in a cylindrical outer shape having an axis extending in the axial direction of the camshaft and disposed in the decompression shaft housing recess;
a decompression pin provided on one axial side portion of the decompression shaft so as to protrude radially from the peripheral surface of the decompression shaft;
a decompression cam that is formed on the other side of the decompression shaft in the axial direction and protrude from the base surface of the exhaust side cam;
It is formed in a ring shape or a C shape so as to surround the outer peripheral sides of the camshaft and the decompression shaft, and is provided at a position facing substantially the center portion of the decompression shaft in the axial direction to accommodate the decompression shaft. a decompression holder rotatably held in the recess;
A decompression device that is provided on the outer peripheral side of the camshaft, is connected to the decompression pin, and is displaced in a direction away from the camshaft due to centrifugal force generated when the camshaft rotates, thereby rotating the decompression shaft via the decompression pin. an arm;
a biasing member that biases the decompression arm in a direction to approach the camshaft;
Either or both of the inner peripheral surface of the decompression holder and the outer peripheral surface of the camshaft are provided with the decompression holder from one end side of the camshaft when the decompression holder is attached to the camshaft. A pin passage portion, which is a groove or recess for passing the decompression pin provided in the decompression shaft disposed in the shaft housing recess, when the decompression shaft is moved to the outer peripheral side of the axially substantially central portion of the decompression shaft beyond the decompression pin. A valve train, characterized in that is formed. A decompression shaft covering groove is formed on the inner peripheral surface of the decompression holder to cover a portion protruding from the decompression shaft housing recess at a substantially central portion in the axial direction of the decompression shaft,
The pin passage portion is a groove formed in the inner peripheral surface of the decompression holder, and the groove is adjacent to the decompression shaft covering groove in the circumferential direction of the decompression holder and integrated with the decompression shaft covering groove. The valve mechanism according to claim 1, characterized by: The pin through portion is a recess formed in the outer peripheral surface of the camshaft, the recess is on one end side of the decompression shaft housing recess in the axial direction of the camshaft, and the decompression shaft in the circumferential direction of the camshaft. 2. The valve mechanism according to claim 1, wherein the valve train is arranged adjacent to the shaft housing recess and integrated with the decompression shaft housing recess. A decompression shaft covering groove is formed on the inner peripheral surface of the decompression holder to cover a portion protruding from the decompression shaft housing recess at a substantially central portion in the axial direction of the decompression shaft,
The pin through portion includes a pin through groove formed in the inner peripheral surface of the decompression holder and a pin through recess formed in the outer peripheral surface of the camshaft,
The pin passing groove is adjacent to one side of the decompression shaft covering groove in the circumferential direction of the decompression holder and is integrated with the decompression shaft covering groove,
The pin through recess is arranged on one end side of the decompression shaft housing recess in the axial direction of the camshaft and adjacent to one side of the decompression shaft housing recess in the circumferential direction of the camshaft. 2. The valve mechanism according to claim 1, wherein the valve train is integrated with the housing recess.

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